The instant invention relates to a bar screen filter for filtering of solid contaminants from a liquid.
Fixed bar screens comprised of a plurality of parallel, longitudinally extending, transversely spaced bars are known in the art. However, such bar screens generally employ relatively wide interbar spacing and are used only to separate sizeable contaminants from a liquid flowing therethrough. To effect removal of smaller contaminants, the prior art teaches the use of a secondary filter downstream from the bar screen.
For example, U.S. Pat. No. 4,392,952 to Fechter et al discloses a vertical bar screen filter where the cleaning mechanism is of the pivotal type that articulates at the bottom of a stroke.
U.S. Pat. No. 3,093,580 to Siewert teaches a bar screen consisting of a vertical screen which is stationary and a movable screen that moves laterally to remove particles from the fixed screen.
U.S. Pat. No. 4,424,125 Martin discloses a septum into which a traveling conveyer scrapes material. There is no teaching of rakes or knives that pass through the screen.
U.S. Pat. No. 4,184,957 to Botsch discloses a double screen. Rake arms are located on the upstream side of the filter. The bar screen may be inclined or vertically disposed.
U.S. Pat. No. 4,447,323 Jackson discloses a vertical or inclined bar screen with the cleaning mechanism on the upstream side. A watertight gutter carries a pan that carries debris into a trough.
The aforesaid patents all teach the use of relatively coarse spacing of the bars generally in the 1/4" to 1/2" range. All the rakes or cleaning mechanisms are fixed relative to one another. All of the bar screens are vertically disposed or slightly inclined from the vertical.
The bar screen filters taught in the aforesaid patents do not fully satisfy a requirement often found in industry, namely, that such filters screen out relatively fine particles, for example, particles in the 0.010" to 0.040" range. When closely spaced bars are used, the manufacturing tolerance of the bars comes into play. Such fine slots must be cleaned without the cleaning blades encountering interference with the bars due to tolerance stackup, bending, warpage, or other forms of bar distortion.
Another desirable feature of a bar screen filter is that the bar screen be orientated horizontally and that fluid flow be upward therethrough so that debris falls cleanly away from the bars by gravity.
Yet another desirable feature is that the screen cleaning knives be orientated on the downstream side of the bar screen so as to prevent the accumulation of foreign material on the scraper mechanism.
Accordingly, there is a need for a practical bar screen filter that utilizes relatively closely spaced bars, an efficient scraping mechanism utilizing floating knives, or rakes, and an orientation that augments filter efficiency.